The present invention relates to a detector, and more particularly, to a window glass obstruction detector for detecting a foreign object caught in a window glass.
Power window apparatuses, which raise and lower a window glass of an automobile using the driving force of a motor, are conventionally known. The motor is driven by operating a window switch provided, for example, in a side door of the automobile. Some power window apparatuses have an anti-obstruction function. A foreign object such as a finger may be caught between a window glass and the window frame when the window glass is operated to close. If this happens, the power window apparatus with the anti-obstruction function stops the closing operation of the window glass, and then opens the window glass to free the foreign object.
Methods for detecting such obstruction by a foreign object include a “voltage/current detection method” and a “pulse detection method”.
As one example, Japanese Laid-Open Patent Publication No. 9-21274 discloses a detector employing the voltage/current detection method for detecting obstruction by a foreign object. This detector monitors changes in the power supply voltage (or in the motor voltage applied to a motor) and changes in the motor current, and detects an obstruction based on the amount of change in the voltage and the amount of change in the current. To be more specific, when the amount of change in the power supply voltage or in the motor voltage exceeds a preset voltage determination threshold, the detector does not detect obstruction by a foreign object in consideration of the influence of changes in the power supply voltage or in the motor voltage. In this way, the detector avoids erroneous detection of the obstruction. When the amount of change in the voltage is equal to or below the voltage determination threshold and the amount of change in the current is equal to or above a predetermined current determination threshold, the detector determines that a foreign object has been caught and stops or reverses the motor.
As one example, Japanese Laid-Open Patent Publication No. 10-169315 discloses a detector employing the pulse detection method for detecting obstruction by a foreign object. This detector detects obstruction by a foreign object based on a pulse signal. The pulse signal has a cycle proportional to the rotational speed of a motor for operating the window glass. When a foreign object is caught in the window glass, the rotational speed of the motor decreases. When the rotational speed of the motor decreases, the pulse cycle of the motor becomes longer accordingly. The detector detects the obstruction by comparing the amount of change in the pulse cycle (the rotational speed of the motor) per unit time with a preset threshold.
The pulse cycle of the motor also changes as the voltage of a battery for supplying power to the motor changes. Specifically, the pulse cycle of the motor becomes shorter as the battery voltage increases and the rotational speed of the motor increases. The pulse cycle of the motor becomes longer as the battery voltage deceases and the rotational speed of the motor decreases. The battery voltage changes when, for example, impacts or vibrations are generated by opening or closing a door or by driving the vehicle on a rough road. While the window glass is being operated, the pulse cycle of the motor also changes as the battery voltage changes. The detector also considers the influence of such changes in the pulse cycle caused by changes in the battery voltage when determining whether a foreign object has been caught in the window glass. In this way, the detector avoids erroneous detection of the obstruction (i.e., erroneous determination that a foreign object has been caught in the window glass when nothing has been actually caught in the window glass) based on changes in the pulse cycle caused by changes in the battery voltage.
When external loads, such as impacts generated by opening or closing a door and impacts (vibrations) caused by driving the vehicle on a rough road, are applied to the vehicle or when electric loads change, such as when an air conditioner and a car stereo are switched on, the battery voltage and the pulse cycle change suddenly. The above-described conventional detector deals with such sudden changes in the battery voltage and the pulse cycle. In other words, the detector does not detect such sudden changes in the battery voltage and the pulse cycle, which are caused by impacts, vibrations, or the supply of power to the electric loads, as a foreign object obstructing the movement of the window glass.
The conventional detector, however, may fail to avoid erroneous detection when the engine of the vehicle is stopped and the voltage and the pulse cycle change gradually due to the stopped engine. The detector may erroneously detect obstruction by a foreign object based on such gradual changes in the voltage and in the pulse cycle. A complex control program is required for monitoring not only sudden changes but also gradual changes in the battery voltage and the pulse cycle (change amounts per unit time). By considering both the sudden and gradual changes using such a complex control program, erroneous detection of the obstruction may be prevented.
To prevent erroneous detection by considering both the sudden and gradual changes without using a complex control program, the detector may use the same program (i.e., the same detection probability) to execute both an anti-erroneous-detection process for the sudden change and an anti-erroneous-detection process for the gradual change. This structure, however, fails to provide accuracy in either the anti-erroneous detection process for the sudden change or the anti-erroneous detection process for the gradual change. This is because a control program to be used by the detector to detect the obstruction inevitably is a program to be used exclusively in a detection process for the sudden change or in a detection process for the gradual change, or is a program to be used in a detection process for a change that falls between the sudden change and the gradual change. It is difficult to provide accuracy in both the anti-erroneous detection process for the sudden change and the anti-erroneous detection process for the gradual change. It is unrealistic that an anti-erroneous detection process considering both the sudden and gradual changes be realized using a single control program.
If a control program for preventing erroneous detection caused by the sudden change is used in a detection process for the gradual change, the detector may erroneously detect obstruction by a foreign object based on the gradual change. When, for example, the engine is stopped while the window glass is being operated to close and the battery voltage and the pulse cycle change gradually due to the stopped engine, the detector may erroneously detect obstruction by a foreign object based on this gradual change.
If a control program for preventing erroneous detection caused by the gradual change is used in a detection process for the sudden change, the detector may erroneously detect obstruction by a foreign object based on the sudden change. When, for example, impacts are generated by opening or closing of a door while the engine is being operated and the window glass is being operated to close, and the battery voltage and the pulse cycle change suddenly due to the impacts, the detector may erroneously detect obstruction by a foreign object based on this sudden change.
For the reasons described above, it is difficult to provide accuracy in both the anti-erroneous detection process for the gradual change and the anti-erroneous detection process for the sudden change without using a complex program.